It is important that a hearing aid fits well in a subject's ear. Therefore, an impression of the subject's external ear is first made. The impression is then used as a mould for manufacturing an individually adapted ear insert or a shell of a hearing aid.
The impression is usually made by a plug of foam rubber, cotton or the like first being inserted into the auditory canal to protect the eardrum from the impression material and damage during the impression process. A nozzle of an impression gun containing impression material is then inserted into the auditory canal approximately 5-6 mm and the impression material is thereafter injected gently into the auditory canal so that it fills up the space in the auditory canal and starts flowing back out past the tip/mouth of the nozzle. Next, the impression gun is retracted slowly out of the ear while impression material still is supplied. When the entire auditory duct is filled with the impression material, this is allowed to solidify, which usually takes approx. 5 to 10 minutes, whereupon the impression is removed gently from the ear. Also the protecting plug is removed. Next, the ear is inspected to guarantee that there is no impression material left in the ear.
The impression material usually consists of two components, which react when they are mixed, and thereby solidify.
The impression is then used as a mould for manufacturing an individually adapted ear insert. This may, for instance, be carried out by the surface of the impression being scanned by means of a laser, and data from the laser is processed in a computer in order to be transformed into a three-dimensional model. This three-dimensional model may then be used for the manufacture of the individually adapted ear insert.
FIG. 10 shows an example of a device for taking an impression of a subject's ear in the form of an impression gun 10. The impression gun 10 has a holder handle 11 and an operating handle 12. The impression gun 10 also comprises containers for impression material. It is common that the impression material consists of two components that are mixed immediately before or during the introduction into the ear. Therefore, the impression gun shown in FIG. 10 has a first container 13 for a first component of an impression material as well as a second container 14 for a second component of an impression material. These two components are pressed out into the nozzle 15 of the impression gun when the operating handle 12 is moved toward the holder handle 11 and are ejected from the nozzle 15 into a subject's ear for taking an impression of the ear.
The technique for manufacturing ear inserts described above may also be used in the same way for manufacturing individually adapted ear plugs or individually adapted earphones.
There is however a risk of impression material penetrating past the plug intended to protect the eardrum, which risks that the eardrum is damaged when the impression is made or removed from the ear. Therefore, these impressions are made by specially trained personnel being well-acquainted with the risks. If the impression material cannot be removed from the ear after the impression has been made, in the worst case, an operation to remove remaining impression material may have to be made.